What should I do if the ULPA is blocked and cannot be scanned?

Encountering obstruction during on-site leak detection is a common situation in equipment-side projects. Protective nets, diffuser plates, robotic arms, cable trays, and box structures may block the edges of the filter material, glue seams, or installation interfaces, making it impossible for the probe to approach as required.

Occlusion itself is not a problem. The problem is that the positions that cannot be scanned cannot be regarded as qualified by default. Without detecting the position of data, the status is undefined. If these positions are skipped during acceptance, once particle abnormalities occur in subsequent runs, the scope of troubleshooting will be larger. For specific leak detection boundaries, please refer to the relevant instructions for leak detection parts of FFU and EFU with ULPA.

First confirm the occlusion type and scope of influence

The occlusion is different and the processing method is different.

Fixed structural occlusion. Box splicing parts, welded brackets, permanent protective panels. Such structures usually cannot be dismantled on site and need to be addressed from the design stage or using alternative verification methods approved by the project.

Removable parts cover. Diffusion plate, access cover, protective net, temporary support. If such components can be removed before leak detection and reset after leak detection, the occlusion problem can be alleviated. It is necessary to confirm whether disassembly and assembly will affect the sealing state to be verified.

Obstruction of moving parts of equipment. Robotic arms, transmission parts, cables. This type of occlusion may vary depending on the device state. You can try to scan at a specific location of the device or in maintenance mode, but make sure the airflow conditions in this state meet the requirements of the detection method. involving The equipment-side application of EFU equipment-side fan filter unit has many moving parts, and the leak detection path must be planned in advance.

Pipes and cables are blocked. If the air line, liquid line, and motor cables are close to the edge of the filter element, they may block the probe. You can check whether there is room for adjustment or temporarily remove it without affecting functionality.

Record the occlusion location and range. Use diagrams or coordinates to mark the blocked filter surface, glue seam or sealing interface. Explain what the obstruction is, whether it is removable, and what extent it affects. This information is the basis for subsequent evaluation of alternatives.

Prioritize improvement of inspection space or assembly structure

If the obstruction results from structural design, prioritize adjusting the structure or installation sequence rather than directly looking for alternatives.

Reserve the probe channel. During the equipment or cabinet design stage, allow space for the probe to be close to the edge of the filter media and the sealing interface. The channel size is determined according to the detection method and probe shape. There cannot be just a 'visible' gap. involving For ULPA ultra-high-efficiency filter projects, the detection channel can be evaluated together with the product structure.

Designed with removable parts. Design the diffuser plate, protective net, and cover into a detachable structure. They can be removed before leak detection and reset after leak detection. The disassembly and assembly method should be simple, and the sealing and air flow organization should not be affected after reset.

Adjust the installation order. Check for leaks first, then install the blocking parts. For example, after installing the filter element into the box, first scan the interface and edges to confirm that the seal is normal, and then install the diffuser plate or protective net. This sequence needs to be clarified during the planning stage and written into the installation procedures.

Adjust the installation position. If space permits, slightly adjust the position of the filter element or box so that the edges and interfaces are away from the obstruction. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space and limited room for adjustment, but it can reduce occlusion through layout optimization during the design stage.

Supporting For the FFU fan filter unit system, the interface between the unit and the ceiling or bracket must also be considered. Pipelines and bridges above the ceiling may block the interface above the filter element. The leak detection sequence and channels need to be confirmed in advance.

Alternative verification schemes must be approved by the project

If the obstruction does not resolve, alternative verification options may be evaluated, but only if approved by the project documentation and applicable specifications.

Leak detection in sections. Before installing the barrier, inspect the accessible area for leaks. After the shield is installed, use other methods to verify the inaccessible areas, or record them as undetected areas.

Factory report plus installation seal verification. The integrity of the filter element body is supported by a factory leak test report. Leak detection is performed on the installation interface and accessible areas on site, and the factory data is quoted for inaccessible areas of the filter element body. This combination requires the project party to confirm whether it is acceptable. For specific report comparison, please refer to the relevant instructions on the difference between factory leak detection and on-site leak detection.

Indirect verification. The judgment is assisted by data such as air volume, pressure difference, and downstream particle monitoring. These data cannot directly prove that the partial seal is complete, but can be used as a reference for the operating status. If the indirect data is abnormal, further investigation is still required.

The limitations of alternative methods should be clearly stated. What the alternative can and cannot cover, and with what degree of confidence, should be stated in the acceptance record. 'Indirect data is normal' cannot be equated with 'inaccessible area sealing is qualified'.

involving For acceptance of HEPA/ULPA air filters , alternatives should comply with the standards and acceptance conditions adopted by the project. Different levels and different application scenarios have different requirements for leak detection, and the detection range cannot be reduced by itself.

Record and retest

Either way, records must be complete.

Unreachable area records. Location, cause, obstructions, scope of impact, alternative verification methods, project confirmation status.

Inspectable area records. Scan path, detection conditions, leak location and processing results. The data in the inspectable area must be complete, and the inspection of other areas cannot be relaxed just because some areas are inaccessible.

Retest conditions. If the shielding parts are subsequently removed or the equipment structure is changed, additional leak detection should be performed in the original inaccessible areas. The retest conditions should be as consistent as possible with the initial test.

Run trace. For areas not directly tested, monitoring will be strengthened during operation. If particle anomalies or pressure differences occur, these locations should be investigated first. involving The equipment-side items of HEPA high-efficiency filters have the same tracking requirements.

Project judgment example

After the ULPA filter element of a certain equipment is installed in the box, the air outlet surface has a fixed shield. The distance between the shield and the edge of the filter element is small, and the probe cannot approach the surrounding glue seams.

The investigation found that the guard was part of the equipment structure and could not be disassembled on site. After evaluation by the project team, a detachable inspection cover was added during the design stage, corresponding to the filter element's glue seam and sealing interface. When detecting leaks, remove the cover, scan the edges and interfaces, and reset after completion. After resetting, confirm that the cover plate is properly sealed and does not affect the operation of the equipment.

This case illustrates that solving occlusion problems during the design phase is more reliable than finding alternatives after delivery. involving ULPA ultra high efficiency filter or The selection of HEPA high-efficiency filters and detection accessibility should be included in the program evaluation.

Selection and Acceptance Checklist

About Aili Industrial’s detection accessibility cooperation

If it is blocked and cannot be scanned, in many cases it is not a problem with the leak detection method, but rather that the detection channel is not taken into account during the structural design stage. If the filter, box, and installation interface are checked together during the planning stage, there will be fewer inaccessible areas on site.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For equipment-side projects, the internal structure of the equipment, installation space and leak detection requirements can be combined to help confirm the probe accessibility, disassembly and assembly sequence and detection channels. When the filter is matched with equipment such as FFU and EFU, the interface size and sealing structure can be confirmed uniformly, reducing on-site acceptance difficulties caused by structural obstruction.

Providing equipment structure diagrams, installation conditions and leak detection requirements when inquiring will help to consider detection accessibility during the planning stage. The specific testing methods and judgment standards are subject to the project plan.